1. Field of the Invention
The present invention generally relates to a woven fabric which is rendered endless by interdigitating a plurality of loops which are on the two ends of the fabric.
2. Description of the Prior Art
As will be known to those skilled in the art, papermaking machines generally include three sections which generally are referred to as the formation, press and dryer sections. Papermaking fabrics are used to transport the paper product through the various sections of the papermaking equipment. Many papermaking fabrics are woven fabrics comprising a system of warp yarns interwoven with a system of weft yarns.
The woven fabric may be woven as an endless loop and utilized as such so there is no seam. Alternatively, the fabric may be woven to have two ends which are joined at a seam to form the endless loop. Various seams are known in the art, including pin type seams which utilize a joining wire or pintle which is inserted through seam loops at each end of the fabric to render it endless.
One technique of forming a fabric having seam loops is to provide an endless weave wherein loops are formed by weaving stacked weft yarns around a forming wire. U.S. Pat. No. 3,815,645 provides an example of such a weaving technique. A common problem associated with this type of loop formation is non-uniform loop alignment, both in the vertical and horizontal axis, when the forming wire is removed. This misalignment creates seaming loops that are difficult to intermesh on the papermaking machine.
FIGS. 1-3 show representative loop misalignments experienced in common prior art endless woven seams. Generally, as a loom weaves the loops in an endless weave, it naturally offsets the returning weft position slightly from its outgoing weft position. Therefore, it is necessary to maintain the weft yarns in a stacked relationship throughout the fabric through the balanced weave of the warp yarns. The last warp yarn 2, however, is generally not balanced by adjacent yarns on each side and therefore, an unbalanced crimp force is applied to the weft yarns in the loop area, as shown by the arrows in FIG. 2. As a result, the two weft yarn passes which form each loop are not balanced by warps and the loops tend to be misaligned.
A similar misalignment of the loops occurs in flat woven fabrics wherein the tie back portion of the warp yarn is offset from the outgoing portion of the warp yarn during loop formation.
In the present invention, additional cross machine direction (CMD) end yarns are woven in a balanced weave to reduce the unbalanced crimp force acting on each of the seam loops. Thus, the loops are held in better horizontal and vertical alignment.